1 // Copyright 2010 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_PROFILER_CIRCULAR_QUEUE_H_ 6 #define V8_PROFILER_CIRCULAR_QUEUE_H_ 7 8 #include "src/base/atomicops.h" 9 #include "src/globals.h" 10 11 namespace v8 { 12 namespace internal { 13 14 // Lock-free cache-friendly sampling circular queue for large 15 // records. Intended for fast transfer of large records between a 16 // single producer and a single consumer. If the queue is full, 17 // StartEnqueue will return nullptr. The queue is designed with 18 // a goal in mind to evade cache lines thrashing by preventing 19 // simultaneous reads and writes to adjanced memory locations. 20 template<typename T, unsigned Length> 21 class SamplingCircularQueue { 22 public: 23 // Executed on the application thread. 24 SamplingCircularQueue(); 25 ~SamplingCircularQueue(); 26 27 // StartEnqueue returns a pointer to a memory location for storing the next 28 // record or nullptr if all entries are full at the moment. 29 T* StartEnqueue(); 30 // Notifies the queue that the producer has complete writing data into the 31 // memory returned by StartEnqueue and it can be passed to the consumer. 32 void FinishEnqueue(); 33 34 // Executed on the consumer (analyzer) thread. 35 // Retrieves, but does not remove, the head of this queue, returning nullptr 36 // if this queue is empty. After the record had been read by a consumer, 37 // Remove must be called. 38 T* Peek(); 39 void Remove(); 40 41 private: 42 // Reserved values for the entry marker. 43 enum { 44 kEmpty, // Marks clean (processed) entries. 45 kFull // Marks entries already filled by the producer but not yet 46 // completely processed by the consumer. 47 }; 48 V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE)49 struct V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry { 50 Entry() : marker(kEmpty) {} 51 T record; 52 base::Atomic32 marker; 53 }; 54 55 Entry* Next(Entry* entry); 56 57 Entry buffer_[Length]; 58 V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_; 59 V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_; 60 61 DISALLOW_COPY_AND_ASSIGN(SamplingCircularQueue); 62 }; 63 64 65 } // namespace internal 66 } // namespace v8 67 68 #endif // V8_PROFILER_CIRCULAR_QUEUE_H_ 69